Correct Answer: B
Explanation:
Normal metabolism releases mainly acidic materials: carboxylic acids such as lactic acid (HLac). These acids react with hydrogen carbonate ion and form carbonic acid.
The carbonic acid is converted through the action of the enzyme carbonic anhydrase into aqueous carbon dioxide.
An increase in CO2(aq) concentration stimulates increased breathing, and the excess carbon dioxide is released into the air in the lungs.